1. Field of the Invention
The present invention relates to an antifouling coating composition, and more particularly to a coating composition which is coated on underwater structures such as ships, port facilities, buoys, pipelines, bridges, submarine stations, submarine oil field excavation facilities, water conduit raceway tubes in power plants, cultivating fishing nets, stationary fishing nets and the like to provide an antifouling coating which is formed on the surface of the underwater structure and which is suitable for preventing underwater living things from adhering and growing on the surface of the underwater structure.
2. Description of the Prior Art
Biofouling, the growth of barnacles, seaweeds, tubeworms and other marine organisms on the hulls of ocean-going vessels, and other underwater structures, cause the international marine community billions of dollars a year. In the case of ocean-going vessels, most of this money goes for the extra fuel needed to overcome the increased drag on vessels. Some of it is spent for hull cleaning and repainting and for the upkeep on propulsion equipment. Of the total amount of money, a tiny amount is invested in the search for better antifouling inhibitors.
One currently used hull antifouling coating contains species such as tributyltin compounds or copper oxide and function through leaching of the toxicant into the marine environment. The resulting environmental hazards of introducing such toxicants into the marine ecosystem include disruption of natural ecocycles for many commercially important shellfish and pollution of entire food chains. The removal and disposal of toxicant-containing coatings from ships and other structures also pose separate environmental hazards, driving up the cost of refurbishment.
An alternative approach is to use acrylic acid monomer compositions which are water soluble, i.e., a polyester resin with an acrylic acid group. Such coatings include a biocide, which after a certain amount of time becomes inactive. The composition, because it is water soluble, wears off over time, i.e., is ablative, and exposes new and active biocide at the surface. Such a composition is known as a self-polishing composition. Thus the alternative approach has been to employ a polymeric coating to function as a fouling release coating. Poly(dimethylsiloxane) (PDMS)-based coatings have properties which meet some of those requirements. On the other hand, as noted, studies have shown that such a cured PDMS material becomes unstable when immersed in water for three months.
Another specific approach involves the use of a composition containing a majority by weight as resin-solid content a reaction-curable silicone resin composition, a silicone resin having the specific average molecular weight and viscosity and an alkoxy group at its molecular terminal. While such a composition exhibits non-toxic characteristics, it is silicone based and in addition to the discussed disadvantages, subject to premature wear requiring frequent maintenance in the form of reapplication of the coating.
In accordance with the invention, the disadvantages of the prior art are avoided and an antifouling coating composition which is a silicone modified glass, not silicone based, is provided which is extremely effective in preventing fouling, and which is highly durable over time.